The IP Multimedia Subsystem (IMS) is an architectural framework for delivering Internet Protocol (IP) multimedia services. Historically, mobile phones have provided voice call services over a circuit-switched-style network, rather than strictly over an IP packet-switched network. Alternative methods of delivering voice or other multimedia services over IP have become available on smartphones (e.g. VoIP applications), but they have not become standardized across the industry. The IMS is an architectural framework to provide such standardization.